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. 2002 Feb;128(2):400–410. doi: 10.1104/pp.010832

Figure 6.

Figure 6

Electrophysiological characterization of a tobacco cyclic nucleotide-gated channel (“NtCBP4”) expressed in oocytes. All recordings were made in the two-electrode configuration, and are presented without leak subtraction. Command voltages were applied in 20-mV steps between −60 and −160 mV. In all cases, [dibutyryl-cAMP] was 5 mm, and the standard oocyte bath solution was used (i.e. with 96 mm K+). A, Current-voltage relationship of NtCBP4 currents. NtCBP4 showed no (inward) currents before addition of dibutyryl-cAMP to the perfusion bath solution (▴). After application of dibutyryl cAMP to the perfusion bath, currents were monitored over 20-min intervals (data not shown), and reached maximum values by (approximately) 60 min (●) in this experiment. Water-injected oocytes displayed no inward currents after exposure to dibutyryl-cAMP for 60 min (○). Results are presented as means (n = 4) ± se. The insert shows representative time-dependent currents recorded from oocytes expressing NtCBP4 before (bottom of insert) and 60 min after addition of dibutyryl cAMP (top of insert). B, Increase of cAMP-activated NtCBP4 currents over time. Time-dependent current recordings are shown for two oocytes expressing NtCBP4. In one case (cell 1), current is shown to be greater at 60 min than that recorded after 30-min incubation in perfusion bath solution containing dibutyryl-cAMP. In the case of the second cell, noticeable currents were recorded only after 100 min incubation in dibutyryl-cAMP; these currents were substantially lower than those recorded from cell one, however. C, Reversal of cAMP activation of plant cngc currents. The top time-dependent currents were recorded from an oocyte expressing NtCBP4 before addition of dibutyryl-cAMP to the perfusion bath solution. The middle current recordings were made 60 min after exposure of the oocyte to dibutyryl-cAMP. Shortly after these currents were recorded, dibutyryl-cAMP was removed from the perfusion bath solution; the recordings at the bottom of the figure were made 30 min after removal of dibutyryl-cAMP.